Radio antenna system



July 24, 1956 T. J. DYLEwsKl RADIO ANTENNA SYSTEM 2 Sheets-Sheet 1 FiledAug. 25 1951 9 ff m m I @RM HWS 5M l E i 27III'I'I I8 2O 22 Z4- o O 0 IlJ o ra wf 757676' OPE/V CHM )d0/V 3.9 50er/aci 4j 3.9

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United States Patent O RADro ANrnNNA SYSTEM Thaddeus J. Dyiewski,Chicago, Ill., assignor to Radio Corporation of America, a corporationof Delaware Application August 25, 1951, Seria] No. 243,628

Claims. (Cl. 343-845) This invention relates to radio antennas and moreparticularly to antennas adapted to be operated at a number offrequencies over a wide frequency band.

When the frequency of operation of a radio antenna is varied, theeffective series resistance and reactance at the antenna terminals varycyclically, having alternate high and low values. In arrangementsheretofore used and known in the art, this variation in antennaresistance and reactance with change in frequency make it necessary toprovide tuning, loading, or matching apparatus between the radioreceiver or transmitter and the antenna to eifect an elhcientinterchange of energy between the antenna and the radio transducerapparatus for all frequencies at which it is desired to operate thesystem. Such arrangements suffer from the disadvantages of beingcomplicated and expensive.

An object of this invention is to restrict the antenna terminalresistance and reactance to a small range of values.

Another object of this invention is to minimize and simplify antennatuning, loading, or matching apparatus between the antenna and the radioreceiver or transmitter.

Brietiy, in accordance with the present invention there is provided anantenna consisting of an extended conductor over a ground plane, withfeed terminals for radio receiver or transmitter apparatus at one endand a switching device between the antenna and ground at the oppositeend. When the switch is open, the antenna terminal resistance andreactance vary cyclically with frequency. When the switch is closed, theantenna terminal resistance and reactance still vary cyclically, but thefrequencies at which high and low values of terminal resistance andreactance occur are transposed; that is, with the switch closed, highvalues of terminal resistance and reactance occur at those frequenciesat Which low terminal resistance and reactance result when the switch isopen, and vice versa.

By operating the antenna with the switch closed over a certain band offrequencies, and with the switch open over an adjacent band offrequencies, the antenna terminal resistance and reactance values can berestricted to a smaller range of variation. The selection of either highor low terminal resistance and reactance values will depend upon thecharacteristic impedance of the transducer apparatus (transmitter orreceiver) to which the antenna is connected.

A more complete understanding of the operation and features of theinvention may be gained from a reading of the following description inconnection with the accompanying drawing in which:

Fig. 1 is a schematic diagram of an arrangement of the antenna of thisinvention;

Fig. 2 is a graphical plot of the variation of the reactance of theantenna as the frequency is varied, showing the far end both open andshorted;

Fig. 3 is a graphical plot of the variation of the antenna resistance asthe frequency is varied, showing the far end both open and shorted;

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Fig. 4 illustrates a cam surface which may be used in connection withthe tuning mechanism of the radio receiver or transmitter of Fig. 1 toautomatically open and close the switch at the far end of the antenna;and Fig. 5 is a schematic diagram according to this invention using acam surface like that of Fig. 4 in connection with the tuning mechanismof a radio receiver or transmitter.

In Fig. 1 an antenna conductor 11 is shown disposed over a conductiveground plane 13. The antenna conductor 11 may be parallel to or at anacute angle to the ground plane 13. One end of the antenna conductor 11is connected to a terminal 15, and another terminal 17 is electricallyconnected to the ground plane 13. These antenna input terminals 15, 17are adapted to have connected thereto a radio transducer apparatus 19,for example a radio transmitter or receiver. At the other end of theantenna conductor 11 a switch or switching device 21 is arranged toconnect the remote end of the antenna conductor 11 directly to theground plane 13. The ground plane 13 may consist of the earth, acounterpoise, the electrically conductive structure of an aircraft,ship, vehicle, or fixed installation, or other electrically conductivesurfaces, frameworks, or bodies in the near zone of the antenna whichjointly or severally complete the conduction circuit of the antenna.

The switching device 21 may be a simple manual switch controlled at theend of the antenna 11 remote from the radio transducer apparatus 19 butpreferably is controlled by a relay 23 which may be actuated by a switchkey 25 at the location of the radio transducer apparatus 19 to supplythe necessary operating current over a pair of conductors 29 from asource of potential 27, such as a battery, generator, or the like. Thepath from the remote end of the antenna 11 through the switch 21 to theground plane 13 may be considered a non-dissipative connection, that is,one having a negligible resistance component.

Although the antenna conductor 11 is shown on the drawing as inclined atan angle to the ground plane 13, it will be understood that similarvariations of antenna terminal resistance and reactance obtain Withother coniigurations such as parallel to the ground plane 13, and thatthis invention is operable with other geometric patterns of antennaconductors Where the ground plane 13 is in the near zone of the antennaconductor 11.

In an antenna in accordance with this invention for installation on anaircraft, the following dimensions are representative.v The length ofthe antenna conductor 11 may vary between 25 and 85 feet, depending onthe type and size of the aircraft upon which the antenna is installed.For aircraft communication in the operating frequency band from 2 to 24megacycles, the wavelength of the free space wave varies from 41 feet toapproximately 492 feet. installations will be longer than one wavelengthat the highest frequency in the operating range, while at the lowestfrequency it will be a fraction of one wavelength.

The switching device 21 is preferably mounted in a rear support memberwhich is secured to the rudder support or vertical stabilizer of theaircraft at a point from 5 to 30 feet above the fuselage of theaircraft. The antenna conductor 11 is customarily made of copper-cladsteel wire of No. 10 gauge which is covered with a polyethylene coatingto prevent corrosion. The spacing of the antenna conductor 11 from thefuselage of the aircraft at the end nearest the radio transmitter andreceiver apparatus is usually somewhat smaller than that at the remoteend. It may be, for example, from less than 2 to'more than 6 feet abovethe fuselage or conductive surface of the aircraft. This dimension alsodepends upon the type of aircraft on which the antenna of this inventionis installed It will thus be seen that the antenna on some I and may bedetermined by optimum measurements ob-l tained during a trial and errorprocedure.

Referring now to Fig. ,2, which is a graphical representation of thevariation of the reactance of an antenna as the frequency is varied;there are shown two curves. One curveLrepresented by an open pair oflines, shows the variation of reactance at the antenna terminals 15, 17V

when the remote end of the antenna conductor 11 is open or ungrounded.It will be noted that the curve for the open end condition varieswidely, extending from about 10,000 ohms positive ,reactanceY to 10,000ohms negative reactance with a very steep slope portion between theseextremes. A second curve in Fig. 2, the area of which is hatched andlabeled with the reference character 33, illustrates the limits ofvariation of reactance of the antenna of Fig. 1 at the treminals 15,117with the far end shorted by the switching device 21.

It will be seen that the curves 31, 33 of Fig. 2 are similar in shape,but corresponding portions of their slopes occur at different pointsinthe frequency baud.

The curves of Fig. 2 represent actual data taken from an antenna havinga length of 50 feet, spaced 8 feet above and parallel to a ground plane,and operated over a frequency range from 2 to 24v megacycles. One of thefactors determining the magnitude of variation of reactance is thespacing of the antenna conductor 11 from the ground plane 13. Curveslike those shown in Fig. 2 will be obtained for all reasonable spacingsof antenna and ground plane. A

Fig. 3 shows a graphical representation of the variai tion of theantenna resistance as the frequency is varied,

with one curve 35 representing the conditions at the antenna terminalswhen the far end is open, and a second curve'37 representing theconditions at the antenna terminals when the far end is shorted to theground plane 13. The curve 35, 'indicated by an open pair of lines,represents the antenna resistance over a band of frequencies from 2 to24 megacycles with the far end open, that is, not connected to ground.It will be noted that the curve 35 has three low resistance portions andtwo very high resistance portions. The second curve 37, the area ofwhich is hatched, has three high resistance portions in the bandoftfrequencies shown, but these occur at frequencies different from thevery high resistance portions of the rst curve 35.

The data from which the curves of Fig. 3 were plotted were obtainedexperimentally under `conditions identical with thosedescribed above `inconnection with Fig. 2.

By operatingover a part of the frequencyA band with the switch 21 ofFig. 1 openV at the far end of the antenna 11, and over anotherV portionof the band with the switch 21 at the far end of the antenna closed toshort-circuit the remote end, the rangeY of variation of antennaresistance and reactance can be greatly'restricted.

The tuning and matching apparatus necessary lin such a system can begreatly simpliedand minimized by restricting the variation of resistanceover the band to a narrower range than is vobtainable Vwithoutswitching, for example to the range from t0 1,000 ohms. This isaccomplished in accordance with this invention by operat- Ving theapparatus with Vthe're'rnote end of the antenna 11 short circuited overthe portion from 2 to approximately 3 megacycles, open-circuited fromapproximately 3 to approximately 7 megacycles, short-circuited from thatpoint to about 121/2 megacycles, and so on, always following thoseportions of either the shorted end or the open end curves'in Fig. 2 or 3which fall within the limits of variation tolerable inthe particularequipment withwhich the antenna isassoeiated. Matching apparatus-whichis required to match a reactance variation of 20,000 ohms or an antennaresistance variation of from 1 ohm to 50,000 ohms is of necessity muchmore complicated and expensive than matching apparatus which iscapableof matchinga reactancevariation of only 2,000

4 ohms lor an antenna resistance variation of 10 ohms to 1,000 ohms.

In Fig. 4, there is illustrated a cam surface which may be used incooperation with the tuning mechanism of the radio receiver ortransmitter 19 to control the opening and closing of the switch 21 atthe Vfar end of the antenna 11 shown in Fig. 1. The cam surface isindicated generally by the reference characters 39 and 41 and isrepresented for the same frequency range and conforms to the abscissascale .of Figs. 2 and 3 shown immediately above. The lower or indentedportions 39 of the surface allow a cam follower to open the contacts ofthe switch key 25 of Fig. 1. When the cam follower, which cooperateswith the cam surface shown in Fig. 4, engages the raised portions 41 ofthe cam surface, the contacts of the switch key 25 will be closed, whichin turn actuates the relay 23 of Fig. 1 to short the remote endreversing the indented portions 39 and the raised portion 41 Vof the camsurface shown in Fig. 4.

Fig. 5 shows'the antenna of this invention installedl on an aircraftwhich utilizes the cam arrangement of Fig.

4 in cooperation with the tunning mechanism of a radio The cam surface39,I

receiver transmitter 19 of Fig. 1. 41 is shown on a shaft 43 whichoperates in cooperation with or controls a tuning element, such as avariable capacitor 45 in the radio apparatus'19. A cam follower 47engages the cam surface 39, 41 and, by the movement of the cam follower47, determines whether the contacts of the switch key 25 are kopen orclosed for the particular tuning adjustment controlled by` the shaft 43.The switching device 21 is shown in this figure as contained in theVvertical stabilizer ofV an aircraft having a conductive surface 13' asdescribed above in conjunction with Fig/1. As indicatedschematicallyinFig. 1, the antenna conductor 11 is maintained in insulated relationshipto the surface of the aircraft or ground plane 13 of Fig. 5.

Instead of the cam control of the switching device 21,

the actuation of the switch 21 at the remote end of the' antenna may beperformed by sensing the voltage appearing across the antenna terminals15, 17 when the antenna is being used for transmitting. The voltage atthe antenna terminals 15,' 17 will change throughout the band due to thevariation of theV antenna resistance and reaetance. At a frequency whichhas been selected for transmitting, the voltage across the antennaterminals 15, 17 may be compared either manually or automatically forboth'open and closed positions of the switch 21 with the optimumtransmitter output voltage, and the` switch position which gives avoltage more closely approximating the value of the optimum outputvoltage is selected. v

It will thus be seen that the arrangement of this invention permits theluse of a single antenna for transmitting or receiving any' of a greatnumber of frequencies over a very wide frequency band. By operating theantenna associated therewith, said radio transducer apparatus beingcoupled to one end of said antenna conductor and to said conductivesurface, switching means directly connected between the other end ofsaid conductor and said conductive surface, and control means for saidswitching means actuated by said tuning means of said transducerapparatus.

2. An antenna switching system as defined in claim 1 in which saidcontrol means comprises a cam surface mechanically coupled to saidtuning means, a keying switch under the control of said cam surface, areiay operative upon the closing of said keying switch to close contactsconstituting said switching means.

3. An antenna switching system as defined in claim 2 in which saidantenna conductor has a length exceeding one wavelength at the highestoperating frequency and less than one wavelength at the lowest operatingfrequency.

4. An antenna switching system as defined in claim 2 in which saidconductive surface comprises the conductive surface of an aircraft.

5. An antenna system comprising a conductive surface, an elongatedconductor extending in a straight line from one end thereof to the otherand mounted in spaced relation with said conductive Surface, antennaterminals for connection to a radio equipment including a terminalconnected to said one end of said conductor and a terminal connected toan adjacent point on said conductive surface, and a switch having aclosed position connecting the other remote end of said conductor to apoint on said conductive surface adjacent said remote end, and having anopen position completely isolating said remote end of said elongatedconductor.

6. An antenna system as defined in claim 5, wherein said points on saidsurface are spaced by substantially the same distance as the length ofsaid conductor.

7. An antenna system as defined in claim 5, wherein said conductor has alength exceeding one wavelength at the highest operating frequency andless than one Wavelength at the lowest operating frequency.

8. An antenna system as defined in claim 5, wherein said conductivesurface comprises the conductive surface of an aircraft.

9. An antenna system as defined in claim 5, wherein said straight wireconductor generally forms an acute angle with said conductive surface.

10. An antenna operable at a plurality of frequencies over a frequencyrange from approximately 2 to 24 megacycles comprising an elongatedconductor having a length of from 25 to 85 feet, a ground planecomprising a conductive surface of an aircraft in the near Zone of saidantenna conductor, radio transducer apparatus having tuning meansassociated therewith, said radio transducer apparatus being coupled toone end of said antenna conductor and to said conductive surface,switching means directly connected between the other end of saidconductor and said conductive surface, and control means for saidswitching means actuated by said tuning means of said transducerapparatus.

References Cited in the tile of this patent UNITED STATES PATENTS2,008,522 Taylor June 16, 1935 2,122,902 Whistlecroft July 5,` 19382,214,830 Carlson Sept. 17, 1940 2,562,296 Christensen et al July 31,1951 FOREIGN PATENTS 500,528 Great Britain Feb. 10, 1939

